It is desired in a future hydrogen energy utilizing society to establish a convenient hydrogen energy system from which the hazardous nature of hydrogen explosion is removed to develop the safety of the hydrogen energy system. It is required that the hydrogen gas sensor is configured such that the hydrogen gas amount leaked in air can be detected at once and the structure of the hydrogen gas sensor can be simplified, and the reliability of the hydrogen gas sensor can be enhanced.
A conventional hydrogen gas sensor is configured on the detecting principle of semiconductor type, ionization type or combustion type, wherein the hydrogen amount is detected indirectly by utilizing the carrier concentration (semiconductor type), the ion concentration (ionization type) or the reaction heat (combustion type, or the hydrogen gas is burned to measure the vapor pressure) which can be defined as an extensive physical value, thereby to be converted into the corresponding electric value. With the conventional hydrogen gas sensor, therefore, it takes longer period of time to detect the hydrogen gas, e.g., by 100 seconds. Particularly, with a hydrogen gas sensor which is to be utilized in a hydrogen leak alarm system, it is required that the hydrogen gas sensor is configured so as to detect the hydrogen gas concentration within a low concentration range below the explosion limit and shorten the period of time in hydrogen detection.
With the conventional (semiconductor type, ionization type or combustion type) hydrogen gas sensor, since the hydrogen gas concentration is detected by utilizing the carrier concentration, the ion concentration or the reaction heat as a hydrogen gas detecting signal, the hydrogen detection requires a large detecting area. In this point of view, the detection precision and sensitivity of the hydrogen gas depends on the structure, the shape and the electrode size of the hydrogen gas sensor, so that the reduction in size of the hydrogen gas sensor is restricted. Moreover, the conventional (semiconductor type, ionization type or combustion type) hydrogen gas sensor may suffer from environmental gases. Particularly, when the hydrogen gas sensor is employed in the atmosphere containing gasoline, hydrocarbon and alcohol which contain hydrogen elements, the hydrogen gas sensor may respond to the hydrogen-based gases, thereby to deteriorate the reliability of the hydrogen gas detection.
In this point of view, new electrochemical gas sensors have been developed and practically used, in substitution for the above-mentioned conventional hydrogen gas sensors. The new gas sensors can be classified as electromotive force measuring type hydrogen gas sensors and current detecting type hydrogen gas sensors. With the former type hydrogen gas sensors, as disclosed in Patent Publication No. 1 and 2, a hydrogen gas electrode is prepared as a standard electrode which is configured on the hydrogen standard gas pressure, and a detecting electrode is prepared as an operating electrode for measuring the gas to be detected (hydrogen gas), wherein the difference in potential between the hydrogen gas electrode and the detecting electrode is measured as the output of the hydrogen gas sensor corresponding to the hydrogen gas concentration.
With the hydrogen electrode, the atomic hydrogen exists sufficiently on the electrode surface to form the standard potential of the electrode. Under the condition, when hydrogen gas contacts with the detecting electrode to be dissociated into atomic hydrogen, the detecting electrode exhibits an electric potential in proportion to the amount of the atomic hydrogen, and the difference in potential between the hydrogen gas electrode and the detecting electrode is detected as the function of the hydrogen gas concentration. In other words, with the new hydrogen gas sensors, since the detecting hydrogen gas pressure is measured in comparison with the standard hydrogen gas pressure, both of electrodes must be disposed independently in the standard hydrogen gas atmosphere and the detecting gas atmosphere, so that another “standard hydrogen gas pressure room must be provided in addition of the detecting gas pressure room. In this point of view, the hydrogen gas sensors are required to be enlarged in size and the use condition and the like of the hydrogen gas sensors are restricted.
With the current detecting type hydrogen gas sensors, the current value is classified as an extensive physical value, so that in order to realize a high precise measurement using the hydrogen gas sensors, the areas or the volumes of the hydrogen gas sensors must be enlarged and external power supplies can be provided for the hydrogen gas sensors.
[Patent Publication No. 1]    Japanese Patent Application Laid-open No. 2003-270200
[Patent Publication No. 2]    Japanese Patent Application Examined Publication No. 5-663